This invention relates to a device for and a method of discriminating a signal with a specific frequency out of a current composed of two or more superimposed current components having different frequencies.
A conventional device generally used for obtaining the signal of a current component to be detected out of a current which is composed of two or more current components with different frequencies employs a transformer or a shunt as the pickup and, in the after stage, a frequency filter circuit or the like.
In the above-described conventional signal discriminator, the signals which have passed the transformer or the shunt can contain besides the signal components noise components, so that a satisfactory S/N (signal to noise) ratio is not to be expected. Therefore, it is necessary for the frequency filter provided in the after stage to be highly efficient.
This naturally results in a relatively large apparatus, which also leads to high cost. Further, when a shunt is employed, a sufficient electrical isolation cannot be effected between the circuit from which signals are to be detected and the pickup. Accordingly, the apparatus is limited in its scope of application. It is difficult, for example, to apply it to a high-tension circuit.